Meaning of INITIAL in English

I. i ‧ ni ‧ tial 1 S3 W2 AC /ɪˈnɪʃ ə l/ BrE AmE adjective [only before noun]

[ Date: 1500-1600 ; Language: Latin ; Origin: initialis , from initium 'beginning' , from inire 'to go in' , from ire 'to go' ]

happening at the beginning SYN first :

an initial investment of £5000

initial stage/phase/period

the initial stages of the disease

The initial response has been encouraging.

II. initial 2 BrE AmE noun [countable]

1 . the first letter of someone’s first name:

‘Can I have your initial, Mr Davies?’ ‘It’s G, Mr G Davies.’

2 . initials [plural] the first letters of all your names in order:

His initials are DPH: they stand for David Perry Hallworth.

III. initial 3 BrE AmE verb ( past tense and past participle initialled , present participle initialling British English , initialed , initialing American English )

[transitive] to write your initials on a document to make it official or to show that you agree with something ⇨ sign :

The two countries have initialled a new defence co-operation agreement.

Longman Dictionary of Contemporary English.      Longman - Словарь современного английского языка.