My copy of DOC 8168 (Fifth edition – 2006) defines STAR & SID as follows:
Standard instrument arrival (STAR). A designated instrument flight rule (IFR) arrival route linking a significant point, normally on an ATS route, with a point from which a published instrument approach procedure can be commenced.
Standard instrument departure (SID). A designated instrument flight rule (IFR) departure route linking the aerodrome or a specified runway of the aerodrome with a specified significant point, normally on a designated ATS route, at which the en-route phase of a flight commences.
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DOC 8168 does not define the terms "arrival" and "departure" - I take it they consider them axiomatic [Self-evident or unquestionable].