firm, good, secure, solid (esp. AmE), strong, tight
crushing, death, iron, painful, vice-like/vise-like
Her upper arms were seized in an iron grip.

gentle, loose, weak
comfortable

have
He still had a firm grip on my arm.

get, take
Taking a tight grip on the hook, he began to pull it closer.

keep
Keep a secure grip on the rope at all times.

lose
She slipped and lost her grip of the rope.

strengthen, tighten
Robert tightened his grip on her shoulder.

loose, loosen, relax, release, slacken
adjust, change, shift

tighten
She felt his grip tighten painfully on her wrist.

loosen, relax, slacken
His grip slackened and she tore herself away.

in a/sb's grip
Hold the microphone in a firm grip.
She was powerless in his iron grip.

grip on
She relaxed her grip on the door frame.

break sb's grip
He finally broke her grip and escaped.

firm, iron, powerful, strong, tight, vice-like/vise-like
tenuous
She has a tenuous grip on reality.

death, icy

have
The Church does not have a strong grip on the population.

get, take
The government needs to get a grip on this problem.
Get a grip! (= take control of yourself, your life, etc.) (informal)

keep, maintain
We need to keep a tight grip on costs.

strengthen, tighten
They managed to strengthen their grip on the southern part of the country.

loosen
lose (informal)
Sometimes I feel I'm losing my grip (= losing control of my life, etc.)

in sth's grip
Winter still held them in its iron grip.
a country in the grip of recession

grip on
The government does not seem to have a very firm grip on the economy.

come to grips with sth, get to grips with sth (= to begin to take control of sth or understand sth difficult)
I'm slowly getting to grips with the language.