lark
n. countable C2 Proficiency US //ˈɫɑɹk// UK //lˈɑːk// lark
n. a small bird known for its beautiful singing, or a fun activity you do just for a joke. You might do something 'for a lark' if you want to be a bit silly.
n. refers to any of several small songbirds, particularly the Alauda arvensis, or a lighthearted, mischievous adventure. Often appears in the idiomatic phrase 'on a lark' or 'for a lark' to indicate spontaneous fun.
We went for a swim at midnight just for a lark.
The morning air was filled with the sweet, rising song of a lark in the meadow.
What began as a harmless lark among university students quickly escalated into a local scandal that required the dean's personal intervention.
Usage
When referring to a prank or fun activity, it is frequently used with the prepositions 'on' or 'for'.