plac
plac — 構詞成分
1. A borrowed Greek-and-Latin word element that appears at the start of some scient
扁平板；片
扁平、板狀的構詞成分
A borrowed Greek-and-Latin word element that appears at the start of some scientific, medical, and everyday English words, carrying the core meaning of 'flat plate', 'tablet', or 'broad flat surface' — for example, it gives the idea of flatness to 'placoderm' (a fish with flat armour plates), 'placenta' (a flat cake-shaped organ), and 'plaque' (a flat marker or deposit on teeth).
The placoderm was an ancient fish whose body was covered in flat, bony armour plates.
盾皮魚是一種其身體覆有扁平骨板的史前魚類（「plac-」扁平 + 「-derm」皮膚）。
plac- + derma (skin): describes flat armour plates on fish
The placenta is a flat, disc-shaped organ that feeds a growing baby.
胎盤是孕育胎兒的扁平圓盤狀器官（「plac-」源自拉丁文「扁平蛋糕」）。
Latin 'placenta' (flat cake): disc-shaped organ
A silver plaque — a flat plate of metal on a wall — told the story of the old library.
一塊銀色匾額——即牆上的一塊扁平金屬板——記錄了這座老圖書館的故事。
In early development, a placode is a plate-like patch of cells that forms on the surface of an embryo.
在胚胎發育初期，基板（placode）是胚胎表面一個板狀的細胞增厚區域。
Shark skin feels rough because it is covered in tiny scales called placoid scales, each shaped like a flat plate.
鯊魚皮摸起來粗糙，是因為表面覆有無數細小的盾鱗（placoid scale），每片都像一塊扁平的小板。
- platy-
another Greek prefix meaning 'broad, flat' (as in platypus 'flat-footed', platysma 'flat muscle'); 'platy-' suggests width while 'plac-' suggests a flat tablet or plate shape
- lamini-
Latin prefix meaning 'thin layer, sheet' (as in laminate); emphasises thinness and layering rather than a solid flat plate
用法筆記
This is a combining form, not an independent English word. It is only found inside other words (placoderm, placenta, plaque, placode, placoid). Do not confuse this Greek-based combining form (from pláx 'flat', 'tablet') with the unrelated Latin root plac- meaning 'to please, soothe' — words like 'placebo' and 'placate' belong to that separate root and have no connection to flatness.