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Looking for a word (verb or adjective) to describe the process of working on something carefully for a lot of time. It should probably be something close to "ponder", but related to working process, not thinking.
I have been working on this project for a lot of time and it's finally done.
Here either the phrase working for a lot of time should be replaced with a verb.
Or for a lot of time should be replaced with an adverb.