Old hat

From Fresh Dictionary

English

Noun

old hat

1. (uncountable) ((idiomatic{{#if:|, {{{2}}}{{#if:|, {{{3}}}{{#if:|, {{{4}}}{{#if:|, {{{5}}}{{#if:|, {{{6}}}{{#if:|, {{{7}}}{{#if:|, {{{8}}}{{#if:|, {{{9}}}}}}}}}}}}}}}}}}})) something with which one is very familiar, experienced, or skilled

   After years in the industry, accounting is old hat for her.