flow line

flow line — noun

1. a visible band, streak, or texture difference in a rock or metal that shows the

1.nounC1
Definition

a visible band, streak, or texture difference in a rock or metal that shows the direction in which the material moved while it was still soft and capable of flowing.

Example

The geologist traced the flow lines in the granite to see how the magma moved.

flow lines in [rock type] — geology context

Sade noticed that the flow lines in the obsidian all curved toward the same direction.

Common collocations
  • trace flow lines
  • follow flow lines
  • flow lines in [rock/metal]
  • curved flow lines
  • visible flow lines
Synonyms
  • flow banding

    a more specific term for layered colour or texture differences in volcanic rocks; 'flow line' is broader

  • grain line

    used mainly for metals and wood; 'flow line' specifically implies the material was in a plastic state

  • fluidal structure

    a formal synonym in petrology for flow-related textures in igneous rocks

Usage Note

Common in geology for igneous rocks and in metallurgy for forged or rolled metals. The patterns are visible to the naked eye or under low magnification.

Common Mistakes

The flow lines in the ice showed how the glacier moved.
The flow bands in the ice showed how the glacier moved.
'flow line' is a technical term for rock and metal, not for ice or glaciers.

2. a pipe, tube, or open channel that conveys a liquid, typically relying on gravit

2.nounC1
Definition

a pipe, tube, or open channel that conveys a liquid, typically relying on gravity rather than pumped pressure to move the water or other fluid.

Example

The flow line carried rainwater from the roof down to the underground storage tank.

flow line carries [liquid] — conveys by gravity

Meera checked that the flow line was clear of leaves before the rainy season.

Common collocations
  • blocked flow line
  • flow line carries [liquid]
  • clear a flow line
  • clay flow line
  • install a flow line
Synonyms
  • drainage pipe

    more specific — a flow line is not always a drain; it could bring water to a tank

  • gravity pipe

    emphasises the lack of pumping; more technical

  • channel

    broader term; a flow line is a type of channel

Antonyms
  • pressurised pipe

    a pipe that moves liquid under pump pressure, unlike a flow line

Usage Note

Distinguish from sense 1 (geology) and sense 3 (coin-making): this engineering sense always refers to a physical conduit. Frequently found in civil engineering, irrigation, and drainage contexts. The pipe may be open or closed but operates at or near atmospheric pressure.

Common Mistakes

The oil pipeline is a flow line under high pressure.
The drainage ditch is a flow line for stormwater.
A 'flow line' in this sense is unpressurised or gravity-driven, not a pressurised pipeline.

3. one of the very fine, hair-like markings that appear on a struck coin's face whe

3.nounC1
Definition

one of the very fine, hair-like markings that appear on a struck coin's face when the metal spreads outward as the die presses the metal blank during minting.

Example

A magnifying glass shows the flow lines running outward from the coin's centre.

flow lines on a coin revealed by magnification

Karim showed the class how flow lines form when the die strikes the coin blank.

Common collocations
  • visible flow lines
  • flow lines run outward
  • flow lines on a coin
  • authentic flow lines
  • raised flow lines
Synonyms
  • metal flow line

    same concept, sometimes used with 'metal' to distinguish from other senses

  • striation

    a general term for fine lines on a surface; less specific to coin-making

Usage Note

Only applies to struck (hammered or pressed) coins, not to cast coins. Flow lines are a normal result of the minting process and are considered a mark of authenticity for older coins.

Common Mistakes

The flow lines on this coin are casting marks.
The flow lines on this coin are minting marks.
Flow lines come from the striking process, not from casting in a mould.

Synonym discussion

Sense: noun/1

Flow lines, flow banding, grain lines, fluidal structures, and foliation all describe visible patterns in rocks or metals, but their scopes differ. Flow banding is narrower — it refers specifically to alternating layers of different colour or composition in volcanic glass, whereas flow line can also describe a single streak or texture in any plastic solid. Grain line is the broadest term, used for the alignment of crystals in wood, metal, or rock. Fluidal structure is a formal petrological term for any flow-related arrangement in igneous rocks. Foliation describes planar layering in metamorphic rock caused by pressure, not by flow of a plastic solid. For example, a geologist might say: 'The flow lines in the obsidian indicate the direction of the original lava flow,' but would describe the parallel layers in a slate as foliation.

flow bandinggrain linefluidal structurefoliation

Etymology

Old EnglishMiddle EnglishEnglish

Flow line is a compound noun formed in English from 'flow' (from Old English flōwan, meaning to stream or pour) and 'line' (from Old English līne, meaning a cord or stroke). The term emerged in the 19th century as geology and metallurgy developed descriptive terminology for structures visible in deformed rocks and metals. By the early 20th century, it had been adopted in engineering for gravity-driven liquid conduits and in numismatics for the surface markings of struck coins.