What does complemental mean?
Complemental is a formal English adjective describing something that completes or supplies what is missing in another thing, so that the two together form a whole. It functions much like the far more common word 'complementary', and in modern usage the two are essentially interchangeable, though 'complementary' dominates ordinary speech and writing. Complemental survives chiefly in formal, technical, or literary contexts — for example, in older scientific descriptions of angles whose measures combine to form a right angle, or in prose emphasising that two contributions fit together neatly. The word derives from Latin complementum, meaning 'that which fills up or completes', and entered English in the early modern period alongside related terms such as 'complement' and 'completion'. Writers should note that despite its similar spelling, complemental has no connection to 'complimentary', which concerns praise or free items. Choosing complemental signals precision and a slightly elevated register.
adjectiveServing to complete or make up a whole; supplying what is lacking in something else. A rarer, more formal variant of 'complementary'.
- Serving to complete or supply what is wanting in something else; forming a complement.
- (Of angles or quantities) combining to form a complete whole or required amount.
"The two reports were complemental rather than contradictory, each filling gaps the other left open."
"Their skills proved complemental: she handled the design while he managed the engineering."
"In older scientific texts, the two angles are described as complemental when together they form a right angle."
Before 'complementary' took over, English speakers reached for 'complemental' — a word that still lingers in formal prose like a well-tailored spare.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of complemental
Complemental comes from the Latin noun complementum, meaning 'that which fills up or completes', itself formed from the verb complere ('to fill up'), built on the root plere ('to fill'). The word entered English during the early modern period, likely in the seventeenth century, as an adjective formed directly from 'complement'. Its sibling words — 'complement', 'complementary', 'complete', and 'completion' — all trace back to the same Latin root, making them true cognates within English.
How complemental is actually used
Complemental is markedly less common than its synonym 'complementary' and is largely confined to formal, technical, or older writing. It carries no special connotation beyond that of completeness or mutual fitting, but choosing it over 'complementary' can lend a slightly archaic or scholarly tone.
Easily confused with complemental
'Complementary' is the standard everyday adjective meaning completing one another, while 'complemental' is a rarer, more formal synonym of it.
'Complimentary' means given free of charge or expressing praise, whereas 'complemental' means serving to complete something.