1. In an imperceptible manner or to an imperceptible degree
   "the power of the Secretary of State in London increased gradually but imperceptibly"
   - unnoticeably

See also: imperceptible

Antonym: perceptibly

• half-evergreen
• half-free morel
• half-hardy
• half-heartedly
• half-heartedness
• half-holiday
• half-hour
• half-hourly
• half-intensity
• half-length
• half-life
• half-light
• half-mast
• half-moon
• half-pay
• half-pint
• half-price
• half-relief
• half-seas-over
• half-size
• half-slip
• half-staff
• half-term
• half-timber
• half-timbered