接頭 is read as せっとう (settou) and means prefix.
せっとう
settou
せっとうご
prefix
せっとうじ
こんてきすとせっとうぶ
context prefix
そくとうとうちょうせつごうぶ
temporoparietal junction
せっきん
becoming close (i.e. friendly)
せったい
entertainment (of guests; esp. in the corporate world)
せつぞく
changing trains
せっする
to be tangent to
せっしょく
touch
せっせん
close combat
せってん
contact (electrical, etc.)
せっけん
meeting with one's lawyer (while detained or imprisoned)