(astronomy) A predicted line on the Hertzsprung-Russell diagram that relates the effective temperature and luminosity of pre-main-sequence stars at the start of their contraction.

A party held to celebrate a person's birthday.

(statistics) A statistical phenomenon where an individual's likelihood of death appears to increase on or close to their birthday, variously attributed to alcohol consumption, psychological stress, increased suicide risk, and other factors.

plural of birthday party

Unclothed.

plural of birthchild

plural of birthday attack

plural of birthfather

plural of birthgasm

(slang, rare) A childbirth with which the procreator feels sexual pleasure.