There are 2 definitions of fs in English:

fs1

Line breaks: fs

abbreviation

Femtosecond(s).

Definition of fs in:

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Word of the day vituperate
Pronunciation: vɪˈtjuːpəreɪt
verb
blame or insult (someone) in strong language...

There are 2 definitions of fs in English:

FS2

Line breaks: FS

abbreviation

(In the UK) Flight Sergeant.