Whenever means at any time that something happens. Every single time, without exception.
It joins two clauses, as in whenever it rains, the roof leaks. It has a second use meaning at whatever time you like, which is why come whenever is a friendly thing to say. Spoken flatly it becomes dismissive, since answering whenever to a question about timing means you do not much care. Do not confuse it with when ever, written as two words, which is used for emphasis in questions.
1adverbwheneverAt any and every time that something happens.~54%
“Whenever he calls, she is out.”
2adverbwhateverAt whatever time is convenient.~46%
“Come round whenever you like.”
Shares are an estimate: a language model read 13 sentences found in the wild and placed 13 of them on a sense — a count of our sample, not a measurement of English.
Middle English
whan evere
English, today
whenever
From Middle English whan evere, whanne ever, whanne evere, whener, when ever; equivalent to when + -ever.
Etymology from Wiktionary, CC BY-SA