What does the cryptic crossword clue "Give support to ‘ack that came last? (7)" mean?

The wordplay uses a charade (building blocks). END (synonym="END") + ORSE (synonym="ORSE") = ENDORSE The answer is ENDORSE.

Give support to ‘ack that came last? (7)

Guardian Cryptic #29598 | 21 Down | 2025-01-22 flower