1. In an official role
   "officially, he is in charge"; "officially responsible" 
2. With official authorization
   - formally

See also: official

Antonym: unofficially

• attendee
• attender
• attending
• attention
• attention deficit disorder
• attention deficit hyperactivity disorder
• attention span
• attention-getting
• attentional
• attentive
• attentively
• attentiveness
• attenuate
• attenuated
• attenuation
• attenuator
• attercop
• attest
• attestant
• attestation
• attestation report
• attestation service
• attestator
• attested
• attester