It happened in the Seventies (5)

I believe the answer is:

event

I'm a little stuck... Click here to teach me more about this clue!

'it happened' is the definition.
The definition suggests a singular noun which matches the answer.

'in the seventies' is the wordplay.
'in' indicates a hidden word.
'EVENT' is hidden in the letters of 'seventies'.

Can you help me to learn more?

(Other definitions for event that I've seen before include "Something going on", "Incident - final outcome", "case", "Something that happens - part of a programme?", "special occasion".)