定

Rare term

heir(s) apparent (royal succession)

Rare term; Linguistics

quasi-negation (e.g. use of words like 'hardly', 'seldom', 'barely'); weak negation

Rare term

T-square (technical drawing instrument)

Rare term

splitting the bill so that the others end up paying the whole amount; wheedling the others into paying the whole bill

Rare term

colorimetry

Pythagorean theorem

Rare term

radio direction finder

Rare term; Physics

gravitational constant