Hadst at disposal is an archaic way of saying "had at one's disposal." It means to have or possess something that can be used or accessed when needed. There are many synonyms for this phrase including: had available, had access to, had possession of, had use of, had in hand, and had in reserve. These alternative expressions are more commonly used in modern English and are easier to understand. It's important to keep in mind that language evolves over time and some phrases and terminology become outdated. It's always helpful to use language that is clear and concise to ensure effective communication.