ichidan verb
be used to doing; be experienced in
Describes being accustomed to performing an action through repeated experience. Often used with verbs in the continuative form (e.g., 使い慣れる, 書き慣れる).
彼は人前で話し慣れている。
He is used to speaking in public.
このソフトはもう使い慣れた。
I've gotten used to using this software.
Standard spelling using the common auxiliary verb する in its continuative form し plus 慣れる.
Ateji spelling; rarely used in modern writing.
慣れる means 'to get used to' something in general, while し慣れる specifically means 'to be used to doing' an action.
Compound of the continuative form し of する (to do) and 慣れる (to get used to).