dia

through, across

Spelled dia · dia 'through, across, apart'

Greek dia carries things across: a diagonal crosses between corners, diaphanous cloth lets light through, and a diagram marks relationships out.

Words built from it

diatribe — a long, bitter verbal attack
dia- (thoroughly) + tribein (rub) → diatribe (wearing away, time spent, discourse)
diaphanous — light and thin enough to see through
dia- (through) + phainein (show) → diaphanes (transparent) + -ous
diametric — at opposite extremes; completely opposed
dia- (across) + metron (measure) → diametros (diameter) + -ic
diagonal — extending slantwise between corners
dia- (across) + gonia (angle) → diagonios (from angle to angle) + -al
diagnosis — identification of an illness or problem from its signs
dia- (apart) + gignoskein (know) → diagignoskein (distinguish) → diagnosis
diagram — a drawing that explains structure or relationships
dia- (across) + graphein (write, draw) → diagraphein (mark out) → diagramma
dialogue — a conversation or exchange of ideas
dia- (through, between) + legein (speak) → dialegesthai (converse) → dialogos

diarist — Comes from diary plus -ist. Diary traces to Latin diarium (daily record) and dies (day), not Greek dia.