Dear old American keeping one quiet, like Mary? (9)

'like mary?' is the definition.
(deiparous means giving birth to a god)

'dear old american keeping one quiet' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'american' becomes 'us' (abbreviation for United States).
'keeping' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'quiet' becomes 'p' (music symbol for 'piano', ie soft or quiet).
'dear'+'o'+'us'='dearous'
'i'+'p'='ip'
'dearous' enclosing 'ip' is 'DEIPAROUS'.