prior to; before; in advance of
Used in the pattern 〜に先立って to mean 'before something happens' or 'in preparation for something'. Formal and often found in announcements or written instructions.
See also: 先立つ (さきだつ)
Prior to the meeting, we will distribute the materials.
the other day; some time ago; recently
Used as a noun or adverb to refer to a recent past event. Often interchangeable with 先だって (せんだって), but さきだって is less common in this sense. May be considered slightly old-fashioned or dialectal.
See also: 先だって (せんだって)
Ahead of the new fiscal year, the budget proposal was announced.
This is the document I gave you when we met the other day.
前もって is a everyday adverb meaning 'in advance', while 先立って is more formal and typically used in the pattern 〜に先立って before a scheduled event.
先だって (noun/adverb 'the other day') is a homophone of 先立って (verb form meaning 'ahead of, prior to'), and the two are easily confused despite unrelated meanings.
From the verb 先立つ (さきだつ, 'to precede') in its て-form, used as a fixed expression. The second sense likely developed from the idea of something that 'came before' the present moment.