Word slices riddle

Question

With three I am used for cleaning,

with four I am used to kill,

with five I can be pretty quick,

with all seven I am considered weak.

Hint:

The slices may not be in the same order

Answer 1

My answer is:

FRAGILE

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With three I am used for cleaning,

RAG, a cleaning tool.

With four I am used to kill,

FRAG, a hand grenade.

With five I can be pretty quick,

AGILE, quick.

With all seven I am considered weak.

FRAGILE