(ن) رَصَدَ يَرْصُدُ رَصْدًاraṣada yarṣudu raṣdan: to lie in wait, to lie in ambush.
رَصَدٌraṣad (adjective in the sense of an active participle, ism fāʿil; the same for singular, plural, masculine and feminine): those lying in wait, watchers, guards. ﴿يَجِدْ لَهُۥ شِهَابًا رَّصَدًا﴾ (Al-Jinn 72:9)
مَرْصَدٌmarṣad (noun of time or place, ẓarf): place of ambush. ﴿وَاقْعُدُوْا لَهُمْ كُلَّ مَرْصَدٍ﴾ (At-Tawbah 9:5)
مِرْصَادٌmirṣād (noun of instrument, ism ālah, on the pattern of مِفْعَالmifʿāl): instrument for lying in wait; then used for a permanent place of ambush, a lookout. ﴿اِنَّ رَبَّكَ لَبِالْمِرْصَادِ﴾ (Al-Fajr 89:14); ﴿اِنَّ جَهَنَّمَ كَانَتْ مِرْصَادًا﴾ (An-Nabaʾ 78:21)
Form IV (ifʿāl) اَرْصَدَ يُرْصِدُ اِرْصَادًاarṣada yurṣidu irṣādan: to post someone in ambush, to appoint as a watcher; to keep ready for a task. ﴿وَاِرْصَادًا لِّمَنْ حَارَبَ اللّٰهَ وَرَسُوْلَهُۥ﴾ (At-Tawbah 9:107)