Loosen

To make something less tight, fixed, rigid, or restricted.

Reach for it when describing reduced physical tension or a relaxation of control

Warm water will loosen the old adhesive without damaging the tile.

• playful

  untie

  a knot or binding is specifically undone

  not when Untie cannot describe rigid rules or stiff joints.

• everyday

  relax

  muscles, rules, or control become less tense

  not when Relax may happen on its own, while loosen often involves an action on something.

• everyday

  unfasten

  a clasp or attachment is opened

  not when Unfasten is too complete when the fitting should remain attached.

• warm

  ease

  pressure or restriction becomes gentler

  not when Ease does not fit every physical fastening.

• professional

  release

  a catch, pressure, or restraint is removed

  not when Release may free something completely rather than merely loosen it.

• formal

  slacken

  tension or pace is reduced gradually

  not when Slacken can imply declining effort or demand.

• literary

  relent

  a person's strict stance becomes less severe

  not when Relent attributes intention and does not suit objects.

• tighten
• fasten
• restrict

• loosen a knot

  A blunt needle helped loosen a knot in the wet rope.

• loosen restrictions

  Officials may loosen restrictions after infection rates fall.

• loosen stiff muscles

  A short walk can loosen stiff muscles after the flight.