What is the appropriate term for shoes that are not suitable for trekking?

The term "unsuitable" accurately describes shoes that do not meet the requirements for trekking. In this context, 'unsuitable' indicates that the shoes lack the necessary features such as grip, support, and protection that are essential for trekking activities. Trekking shoes typically need to be sturdy, provide good traction, and offer comfort over long distances on uneven terrain. Therefore, if shoes are labeled as unsuitable, it directly conveys that they cannot perform these essential functions, making them inappropriate for the purpose of trekking.

The other options do not specifically convey this meaning. 'Fashionable' refers to style rather than functionality, 'comfortable' speaks to how the shoes feel when worn but doesn’t imply their appropriateness for trekking, and 'durable' relates to the longevity of the shoes but does not address their suitability for a specific activity. Hence, "unsuitable" is the most accurate term for emphasizing that the shoes are not fit for trekking purposes.