Complex nominal groups are common in technical English (i.e., English for Specific Purposes, ESP) since they allow lexical items to be tightly packed into a clause which consequently leads to increased lexical density and syntactic ambiguity. In this paper, we analyse (complex) nominal groups in technical English. We propose that, in addition to context and extralinguistic knowledge (i.e. shared technical background that the ESP teacher does not necessarily possess), the structure of the nominal group--or, more precisely, the position of modifiers within the group also plays a role in resolving of syntactic ambiguity and disambiguation of meaning. Thus, modifiers standing farthest from the head have the least specifying potential and are followed by other modifiers that restrict the meaning of the entire nominal group. In this way, the participle "reciprocating" in "steam reciprocating engine" (vs.*"reciprocating steam engine") is more specific in meaning and is thus positioned closer to the head of the nominal group. Our results indicate the type of modification (i.e. linear or non-linear) lends support to the disambiguation of complex nominal groups. The paper's main contribution is in the field of ESP teacher education in the way that it helps ESP teachers who are not specialists in the field of (marine) engineering to process understand and successfully teach complex nominal groups.