[defrost]

You're correct.

As a native English speaker I was aware of the older meaning, however as someone that often "quickly explains english" to ESL folk and|or non-Commonwealth English backgrounds I went with "tearing paper" as a starting point as it felt more likely to be familiar.

This is consistent with your last paragraph re: modern usage.

I've got a much thumbed multi volume OED edition on my shelves .. it's boggling how many words have half page or more entries with multiple meanings and historical backstory.

[Fluorescence]

Yeah, I look up etymology because I love how there are millennia of human culture condensed in a word as it migrates and evolves across classes, cultures and languages. Will it be Norse, Germanic, Latin or maybe Dravidic? Will it have been loaned from x to y to z and then back to x with new meanings?

I had hoped it might have come from reading rapidly in the days of uncut pages where you have to eagerly tear each new page to read it. But no, lol.