Prefix used in compounds to refer to the previous or most recent instance of a time period, such as 昨年 (last year) or 昨日 (yesterday). Not used as a standalone word.
Last year's sales were the highest ever.
The situation last year was unstable.
昨 marks the immediately preceding time period (昨年 'last year'), while 来 marks the immediately following one (来年 'next year').
作 (さく) means a work, harvest, or craftsmanship, while 昨 (さく) means 'previous' as in 昨年 or 昨夜; they share the same sound but are unrelated in meaning.
last year
last night; yesterday evening
these days; nowadays; recently
last night
last fiscal year; previous academic year
last season; equivalent season last year
last summer; summer of last year
last autumn; last fall
The kanji 昨 is composed of 日 (sun/day) and 乍 (while/although), originally indicating 'the day that has passed'. The reading さく is the on'yomi (Sino-Japanese reading).
two days before yesterday; three days ago
one previous; the one before last
last winter
yesterday evening; last night
last spring; the spring of last year
early yesterday morning
yesterday morning
last period; previous period
yesterday's paper; yesterday's issue
last week