Einstand

Etymology
From, deverbal from.

The tennis use derives from the idea of “equilibrium”, from the obsolete phrase. Contemporary speakers may in this context reinterpret as the unrelated numeral for “one”, by analogy with.

Noun

 * 1) first day, start at a new job or position, debut
 * 2) a small party with food and drink traditionally organized by an employee during their first days at work
 * 3)  deuce