磕

kē

to tap

to knock (against sth hard); to knock (mud from boots, ashes from a pipe etc)

stone (石) + phonetic (盍) = knock against something hard

Stone is the semantic core: knocking or tapping always involves something hard. 盍 mainly contributes the sound kē and does not carry the meaning.

石+盍→磕

盍A classical character meaning 'why not'Phonetic

石StoneSemantic

他不小心把头磕在桌子上了。

tā bù xiǎo xīn bǎ tóu kē zài zhuō zi shàng le。

He accidentally knocked his head against the table.

她把鞋底上的泥磕掉，才走进屋里。

tā bǎ xié dǐ shàng de ní kē diào，cái zǒu jìn wū lǐ。

She knocked the mud off the soles of her shoes before walking inside.

死磕

sǐ kē

(coll.) to fight to the death

磕碰

kē pèng

to knock against

磕磕

kē kē

(onom.) knocking

磕磕巴巴

kē kē bā bā

stammering

磕磕绊绊

kē ke bàn bàn

bumpy (of a road)

磕碜

kē chen

(dialect) ugly; unsightly; shabby

磕糖

kē táng

(slang) to revel in the sight of one's favorite couple being affectionate

磕膝盖

kē xī gài

(dialect) knee

磕头

kē tóu

to kowtow (traditional greeting, esp. to a superior, involving kneeling and pressing one's forehead to the ground)

磕头如捣蒜

kè tóu rú dǎo suàn

lit. to kowtow like grinding garlic (idiom)