Learn Arabic (Modern Standard): يا قائد الجيش، لا تثق بالخصم الغدار والمكار. - O commander of the army, do not trust the treacherous and cunning opponent.

Both words use the فَعَّال pattern, which indicates a habit or an intense degree of a trait. You might recognize this pattern from occupations (like خباز for baker), but here it is used for non-occupational descriptive adjectives. Upgrading the standard active participles غادر and ماكر to غدار and مكار emphasizes that the opponent is habitually treacherous and deceitful.

Why does the word for opponent (الخصم) have the preposition بـ attached to it?

This is because of the verb تثق (you trust). In Arabic, the verb وثق (to trust) is practically inseparable from the preposition بـ. You do not trust someone directly as a direct object; you trust in them. Therefore, 'do not trust the opponent' translates to لا تثق بالخصم.

The root for 'to trust' is و ث ق. Why did the و disappear in تثق, and what is its grammatical mood here?

Verbs that start with و (assimilated or 'mithal' verbs) drop that first letter in the present tense, so it becomes تَثِق. Furthermore, because it follows the negative command لا (the prohibitive 'laa'), the verb is in the jussive mood (مجزوم) and takes a sukun on its final letter, making it لا تَثِقْ.

In the phrase يا قائد الجيش, what case ending does the word قائد take and why?