expression
furthermore; and another thing; even as
Used to add an additional point, often with a nuance of 'on top of that' or 'even while'. Can introduce a contrasting or reinforcing statement. The 'even as' gloss reflects a less common usage where さえに follows a verb in the 連用形 (masu-stem) to mean 'even while doing'.
彼は仕事ができるし、さえに性格もいい。
He is capable at work, and furthermore, he has a good personality.
雨が降っている。さえに風も強い。
It's raining. And another thing, the wind is strong too.
彼女は働きさえに学校にも通っている。
She attends school even while working.