これが私の探していた鍵です。

this (indicating an item near the speaker, the action of the speaker, or the current topic); this person (usu. indicating someone in one's in-group); now; here; I (me); certainly

indicates sentence subject (occasionally object); indicates possessive (esp. in literary expressions); but; however; still; and

I; me; private affairs; personal matter; secrecy; selfishness

indicates possessive; nominalizes verbs and adjectives; substitutes for "ga" in subordinate phrases; (at sentence-end, falling tone) indicates a confident conclusion; (at sentence-end) indicates emotional emphasis; (at sentence-end, rising tone) indicates question

to search (for something desired, needed); to look for; to search (for something lost); to seek (a suspect in a crime)

key; lock

be; is